I measured the TF between the current actuator of the laser and PZT on NPRO to see how much the current actuator changes the frequency.
The result, if the current act on the laser mostly adj Freq or Intensity, is yet to be determined
The current actuator on the laser driver changes both frequency and intensity of the out going beam.
This experiment aims to learn how much the current actuator drives the frequency of the laser compared to the intensity.
1) TF between current actuator (Vact) and NPRO PZT (Vpzt)
The source is split and sent to 1)the current actuator, 2) ref ch A on SR785
The response is picked up at fast mon on FSS loop, the voltage between Vmon is the actual voltage sent to the PZT, see the schematic.
The calibration for NPRO PZT is 3.07 MHz/V
Thus response/ref is chB/chA = Vpzt/Vact. I correct the unit to be Hz/Vact by multiplying the Vpzt by the calibration, 3.07MHz/V. or add the original result (in dB) by 20log(3.07 e6) dB.
2)The TF between the current actuator (ref) and PMC trans PD (resp) was plotted in this entry.
The magnitude on the Y axis is Vpmc_transPD / Vactuator. To correct it to RIN, divide Vpmc by DC value of PMC_trans PD [1.37 V] or subtract 20log[1.37] from the result in (dB).
3) TF between pmc trans PD (ref chA) and PZT (resp chB), see fig 2.
The unit after the measurement is [Vpzt / Vpmc_pd]. To correct it to Hz/RIN, multiply Vpzt by the calibration and divided Vpmc_pd by its DC level,
or add 20log(3.07e6) + 20log(1.37)
To sum up,
1) TF between current act and PZT tells us how much frequency changes when we modulate through current actuator,
2) TF between current act and PMC trans PD tells us how much RIN changes when we modulate through current actuator,
3) TF between PMC trans and PZT tells us what changes more after current act is modulated.
This will be compared with frequency change (calculation) due to RIN-> thermo optic.
Then we can decide if current adj mainly change frequency or intensity.